As you pour more time into an idea, it tends to become more internally consistent, shedding those little contradictions between your acquisition strategy and budget or your tagline and vision. But being consistent isn’t the same as being good.
If you end up having to write a business plan for a competition or a grant, it may be evaluated by someone who doesn’t understand your market in general or your business in particular. In these cases, they’ll use consistency as a placeholder for quality.
While the above is unfortunate, it’s also out of your hands. However, we often make the same mistake ourselves, polishing a plan or idea in a vacuum, finding ways for the pieces to fit together more and more tightly until it has a certain theoretical beauty to it, and then believing in it as if its aesthetics were evidence of correctness. When I used to do game design, I suffered big-time from this bias and would spend ages refining a game mechanic on paper before building a playable prototype. In games, as in startups, this is a huge mistake.
The damage isn’t just the time you waste polishing pre-maturely. You also start yourself down a rotten branch of the decision tree. Once you’ve already invested heavily to concoct something beautiful, your brain flinches at the thought of undertaking a serious re-invention of it.
Throwing out a perfectly consistent idea is like throwing out a perfectly engineered product. Regardless of whether or not it’s actually good, in a “will-people-buy-it” sense, you’ll value it at more than its worth and end up making dumb choices.